Vulcanization process of EPDM valve seat for eccentric butterfly valves

Eccentric butterfly valves, as important equipment in the field of industrial fluid control, have sealing performance that directly depends on the weather resistance, corrosion resistance, and elasticity of the valve seat material. Ethylene propylene diene monomer (EPDM) rubber, due to its excellent ozone resistance, chemical resistance, and low-temperature toughness, has become the mainstream material for eccentric butterfly valve seats.

Through scientific vulcanization process design, the overall performance of the valve seat can be improved to meet the long-term stable operation requirements under complex working conditions.
1. Material Selection and Formulation Design
The performance optimization of EPDM valve seats requires starting from the material formulation. It is recommended to use EPDM rubber with a high ethylene content (65%-70%) in combination with reclaimed rubber, with the proportion of reclaimed rubber controlled at 80%-90% to balance cost and performance. The vulcanization system needs to be flexibly selected according to the working conditions: the sulfur-accelerator system (such as CZ/DM/TMTD composite accelerator) is suitable for conventional working conditions, and its vulcanized rubber tensile strength can reach more than 15 MPa; the peroxide vulcanization system (such as DCP) is suitable for high-temperature and high-pressure scenarios, which can improve the heat resistance of the vulcanized rubber to above 180°C. The reinforcing system mainly uses N550 carbon black, combined with 10%-15% calcium carbonate filler, which can both improve wear resistance and reduce shrinkage.
2. Segmented Mixing Process Control
Mixing is a key link in determining the uniformity of the rubber compound.
A segmented mixing process using an internal mixer is adopted:
In the first stage, reclaimed rubber, activator (3 parts of zinc oxide), solid softener (1 part of paraffin), and ordinary accelerator are added, and the mixing temperature is controlled at 110-120°C;
In the second stage, carbon black and liquid softener (7 parts of paraffin oil) are added, and mixing continues until the temperature reaches 140°C before discharging; in the third stage, sulfur (1.33 parts) and ultra-fast accelerator are added on an open mill, and the mixture is passed through 3-5 times to ensure uniform dispersion. This process can reduce the Mooney viscosity of the rubber compound, improve fluidity, and meet the molding requirements of the complex structure of eccentric butterfly valve seats.

3. Precision Molding and Vulcanization Parameter Optimization
The valve seat molding requires a compression molding process, with the mold preheated to 80-100°C to reduce rubber flow resistance.
The vulcanization process uses a two-stage vulcanization method:
The first stage involves pressurizing at 5MPa on a 160°C flat vulcanizing machine, with the vulcanization time calculated based on the product thickness at "1.5 minutes per millimeter";
The second stage involves post-vulcanization treatment at 170°C for 2 hours to eliminate internal stress and improve compression set performance to ≤15%. For triple eccentric butterfly valve seats, a grinding process is added after vulcanization to ensure a sealing surface roughness Ra ≤ 0.8 μm, meeting the zero-leakage sealing requirements.
4. Key Points of Process Quality Control
Vulcanization Reversion Control: The vulcanization temperature curve is monitored in real time using an infrared thermometer to prevent the temperature from exceeding 175°C, which could lead to vulcanization reversion;
Dimensional Accuracy Assurance: A CNC machining center is used for precision machining of the valve seat sealing surface to ensure a clearance of ≤0.05mm with the butterfly plate;
Performance Testing Standards: Tensile strength is tested according to ISO 527, tear strength according to ISO 34, and a 168-hour hot air aging test is performed according to ASTM D573 to ensure a performance degradation rate of ≤10%.

The vulcanization process of EPDM valve seats for eccentric butterfly valves needs to consider material properties, molding accuracy, and process stability. Through optimized formula design, strict mixing control, precise vulcanization parameters, and full-process quality control, high-performance valve seats meeting the API 6D standard can be produced, providing reliable sealing solutions for petrochemical, power energy, and other fields. With the popularization of CNC machining technology and intelligent vulcanization equipment, this process is continuously upgrading towards automation and high precision.